1. Field of the Invention
This invention relates to turbocharged internal combustion engines and, more particularly, to systems for maintaining power from such engines at pre-set levels.
2. Prior Art
It is well known that atmospheric pressure varies from location-to-location and decreases with an increase in altitude. Internal combustion engines which rely on mixing oxygen with a fuel to produce power operate differently at different atmospheric pressures for the obvious reason that the weight of oxygen available in a given volume of air varies with atmospheric pressure. In engine studies this fact is expressed in terms of intake manifold absolute pressure. A decrease in intake manifold absolute pressure causes a decrease in engine power output. This problem of reduced power with reduced atmospheric pressure is particularly significant in aircraft engine operation, although it is also recognized as a factor in diesel and other engine operation. To overcome this problem, pressurizing the air at the intake manifold has been adopted in many engines, particularly aircraft engines. Pressurizing the air has been achieved by means of rotary compressors driven by exhaust turbines, the latter deriving their power from the flow of exhaust gases from the associated engines.
The speed of such a turbocharger must be regulated to prevent excessive intake manifold pressures, such excessive pressures causing engine over-heating and consequent engine damage. Turbocharger speed regulation is achieved by diverting a portion of the exhaust gases through a wastegate instead of permitting all of the exhaust gases from passing through the turbine. In prior art systems the wastegate actuator was operated by engine oil pressure and positioned the wastegate valve in the exhaust bypass. When engine oil pressure closed the wastegate, all exhaust gases were routed through the turbine giving maximum intake air compression. The amount the wastegate was opened determined the portion of the exhaust gases by-passing the turbine and the portion driving the turbine, and hence, the degree to which the intake air was compressed. The automatic wastegate controller of the prior art mechanically sensed the manifold pressure and adjusted oil pressure to a piston coupled to the wastegate valve. When oil pressure was increased on the piston, the wastegate valve moved toward the "closed" position, and engine output power increased. Conversely, when the oil pressure was decreased, the wastegate valve moved toward the "open" position, and output power was decreased.
The position of the piston attached to the wastegate valve was dependent on bleed oil which controlled the engine oil pressure applied to the top of the piston. Oil was returned to the engine crankcase through two control devices, the density controller and the differential pressure controller. These two controllers, acting independently, determined how much oil was bled back to the crankcase, and thus established the oil pressure on the piston.
The density controller was designed to limit the manifold pressure below the turbocharger's critical altitude, and regulated bleed oil only at the "full throttle" position. The pressure and temperature-sensing bellows of the density controller reacted to pressure and temperature changes between the fuel injector inlet, (if fuel injection was utilized) and the turbocharger compressor. The bellows, filled with dry nitrogen, maintained a constant density by allowing the pressure to increase as the temperature increased. Movement of the bellows re-positioned the bleed valve, causing a change in the quantity of bleed oil, which changed the oil pressure on top of the waste-gate piston,
The differential pressure controller functioned during all positions of the waste-gate valve other than the "fully open" position, which was controlled by the density controller. One side of the diaphragm in the differential pressure controller sensed air pressure upstream from the throttle; the other side sampled pressure on the cylinder side of the throttle valve. At the "wide open" throttle position when the density controller controlled the wastegate, the pressure across the differential pressure controller diaphragm was at a minimum and the controller spring held the bleed valve closed. At "part throttle" position, the air differential was increased, opening the bleed valve to bleed oil to the engine crankcase and re-position the wastegate piston.
This prior art mechanical system for wastegate control was heavy, expensive, slow to respond, ineffective in maintaining the proper air-fuel ratio for high performance and low pollution, as altitude and air density changed and not fail-safe.
Therefore, it is a general object of this invention to provide an improved turbocharger system.
It is a further object of this invention to provide an improved control system for an automatic turbocharger.
It is a still further object of this invention to provide a lightweight, inexpensive, short-response-time wastegate control system for an automatic turbocharger.
It is an additional object of this invention to provide an automatic turbocharger control system which exhibits fail-safe characteristics.
It is a further object of this invention to provide a wastegate control system which will cause an automatic turbocharger to maintain, despite altitude and air-density variations, the proper air-fuel ratio in an associated engine whereby high performance and low pollution are consistently obtained.